linux-kernel - Re: [PATCH v5 0/7] add virt-dma support for imx-sdma

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Date:   Mon, 2 Jul 2018 02:32:05 +0000
From:   Robin Gong <yibin.gong@....com>
To:     "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jslaby@...e.com" <jslaby@...e.com>
CC:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v5 0/7] add virt-dma support for imx-sdma

Hi Vinod,
	Do you have any comment for this patchset? Lucas and Sascha
acked it and tty patch already merged in.

On 二, 2018-06-26 at 17:04 +0200, Lucas Stach wrote:
> Hi Robin,
> 
> I've tested this whole series with the SDMA being used for SPI, UART
> and SSI with no regressions spotted. As this should cover most common
> use-cases, I think this series is good to go in.
> 
> Tested-by: Lucas Stach <l.stach@...gutronix.de>
> 
> Regards,
> Lucas
> 
> Am Mittwoch, den 20.06.2018, 00:56 +0800 schrieb Robin Gong:
> > 
> > The legacy sdma driver has below limitations or drawbacks:
> >   1. Hardcode the max BDs number as "PAGE_SIZE / sizeof(*)", and
> > alloc
> >      one page size for one channel regardless of only few BDs
> > needed
> >      most time. But in few cases, the max PAGE_SIZE maybe not
> > enough.
> >   2. One SDMA channel can't stop immediatley once channel disabled
> > which
> >      means SDMA interrupt may come in after this channel
> > terminated.There
> >      are some patches for this corner case such as commit
> > "2746e2c389f9",
> >      but not cover non-cyclic.
> > 
> > The common virt-dma overcomes the above limitations. It can alloc
> > bd
> > dynamically and free bd once this tx transfer done. No memory
> > wasted or
> > maximum limititation here, only depends on how many memory can be
> > requested
> > from kernel. For No.2, such issue can be workaround by checking if
> > there
> > is available descript("sdmac->desc") now once the unwanted
> > interrupt
> > coming. At last the common virt-dma is easier for sdma driver
> > maintain.
> > 
> > Change from v4:
> >   1. identify lockdep issue which caused by allocate memory with
> >      'GFP_KERNEL', change to 'GFP_NOWAIT' instead so that lockdep
> >      ignore check. That also make sense since Audio/uart driver may
> >      call dma function after spin_lock_irqsave()...
> >   2. use dma pool instead for bd description allocated,since audio
> >      driver may call dma_terminate_all in irq. Please refer to 7/7.
> >   3. remove 7/7 serial patch in v4, since lockdep issued fixed by
> > No.1 
> > 
> > Change from v3:
> >   1. add two uart patches which impacted by this patchset.
> >   2. unlock 'vc.lock' before cyclic dma callback and lock again
> > after
> >      it because some driver such as uart will call
> > dmaengine_tx_status
> >      which will acquire 'vc.lock' again and dead lock comes out.
> >   3. remove 'Revert commit' stuff since that patch is not wrong and
> >      combine two patch into one patch as Sascha's comment.
> > 
> > Change from v2:
> >   1. include Sascha's patch to make the main patch easier to
> > review.
> >      Thanks Sacha.
> >   2. remove useless 'desc'/'chan' in struct sdma_channe.
> > 
> > Change from v1:
> >   1. split v1 patch into 5 patches.
> >   2. remove some unnecessary condition check.
> >   3. remove unnecessary 'pending' list.
> > 
> > Robin Gong (6):
> >   tty: serial: imx: correct dma cookie status
> >   dmaengine: imx-sdma: add virt-dma support
> >   dmaengine: imx-sdma: remove useless 'lock' and 'enabled' in
> > 'struct
> >     sdma_channel'
> >   dmaengine: imx-sdma: remove the maximum limitation for bd numbers
> >   dmaengine: imx-sdma: add sdma_transfer_init to decrease code
> > overlap
> >   dmaengine: imx-sdma: alloclate bd memory from dma pool
> > 
> > Sascha Hauer (1):
> >   dmaengine: imx-sdma: factor out a struct sdma_desc from struct
> >     sdma_channel
> > 
> >  drivers/dma/Kconfig      |   1 +
> >  drivers/dma/imx-sdma.c   | 400 +++++++++++++++++++++++++++------
> > --------------
> >  drivers/tty/serial/imx.c |   2 +-
> >  3 files changed, 235 insertions(+), 168 deletions(-)
> >